The Weather of November 2018

November 2018 was much gloomier than usual. As the northeast monsoon affecting the south China coast was relatively weak and southerlies were dominated in the lower atmosphere, more water vapour was built up and the weather in Hong Kong was cloudier than usual. The mean amount of cloud in the month was 79 percent, 25 percent above the normal of 54 percent and the highest on record for November. As a result, the duration of bright sunshine in the month was only 123.9 hours, about 31 percent lower than the normal figure of 180.1 hours and the eighth lowest on record for November. Despite the gloomy weather, the month was warmer than usual. The mean temperature of 22.9 degrees and mean minimum temperature of 21.4 degrees were 1.1 degrees and 1.6 degrees above the respective normals and were respectively the ninth and fourth highest for November on record. November 2018 was also wetter than usual with the monthly rainfall of 73.4 millimetres, about 95 percent above the normal of 37.6 millimetres. The accumulated rainfall up to November this year was 2151.0 millimetres, a deficit of about 9 percent compared to the normal of 2371.7 millimetres for the same period.

Tropical cyclone Yutu edged north slowly towards the coast of eastern Guangdong and weakened gradually on 1-2 November. It eventually dissipated over the northeastern part of the South China Sea on the morning of 3 November. Under the combined effect of the northeast monsoon and tropical cyclone Yutu, it was windy and dry with sunny periods in Hong Kong on the first day of November. While local winds subsided gradually, it was mainly cloudy with a few rain patches in the next two days.

Affected by the northeast monsoon, winds picked up again with a few light rain patches in Hong Kong on 4 November. As the cloud band covering the coast of Guangdong dissipated gradually, the weather of Hong Kong became generally fine in the next three days. With a replenishment of the northeast monsoon arriving at the coastal areas of Guangdong on the morning of 8 November, there were sunny periods and one or two light rain patches in Hong Kong. The weather of Hong Kong turned cloudier and windier with light rain on 9 - 10 November as winds strengthened from the east. With the easterly airstream moderating gradually, there were sunny periods during the day on 11-12 November. The temperature at the Hong Kong Observatory rose to a maximum of 28.0 degrees on the afternoon of 12 November, the highest of the month. Under the influence of the northeast monsoon, winds picked up on 13 November, the weather remained generally fine apart from a few light rain patches in the morning and at night.

Under the influence of a fresh to strong easterly airstream, the weather of Hong Kong became mainly cloudy with a few light rain patches again on 14 - 17 November. The weather improved with sunny periods during the day on 18 November. With a replenishment of the northeast monsoon reaching the south China coastal areas, it was slightly cooler with sunny intervals in Hong Kong on 19 - 20 November.

A cold front moved across the coastal areas of Guangdong on the night of 21 November. Locally, while there were sunny periods during the day, the weather turned cloudy with a few rain patches at night when winds strengthened from the north. Affected by the northeast monsoon behind the cold front, the weather of Hong Kong became appreciably cooler and drier with sunny periods on 22 - 24 November. With a broad rain bearing cloud band covering southern China, local weather became cloudy and rainy on 25 - 28 November. More than 20 millimetres of rainfall were generally recorded on 25 November. Under the rain, the temperature at the Observatory dropped to a minimum of 17.0 degrees on the morning of 26 November, the lowest of the month. With the cloud band thinning out gradually, sunshine returned on the last two days of the month.

Four tropical cyclones occurred over the South China Sea and the western North Pacific in the month.

Details of issuance and cancellation of various warnings/signals
in the month are summarized in Tables 1.1 to 1.3. Monthly meteorological
figures and departures from normal for November are tabulated in Table 2.

Warnings and Signals issued in November 2018

Table 1.1 Tropical Cyclone Warning Signals

Name ofTropical Cyclone

SignalNumber

Beginning Time

Ending Time

Day/Month

HKT

Day/Month

HKT

YUTU

1

31 / 10

0840

1 / 11

1240

3

1 / 11

1240

2 / 11

0210

1

2 / 11

0210

2 / 11

0810

Table 1.2 Strong Monsoon Signal

Beginning Time

Ending Time

Day/Month

HKT

Day/Month

HKT

22 / 11

0905

22 / 11

1230

Table 1.3 Fire Danger Warnings

Colour

Beginning Time

Ending Time

Day/Month

HKT

Day/Month

HKT

Red

28 / 10

0600

1 / 11

1900

Yellow

11 / 11

0600

11 / 11

1730

Table 2 Figures and Departures from Normal - November 2018

Meteorological Element

Figure of the Month

Departure from Normal*

Mean Daily Maximum Air Temperature

24.8 degrees C

0.7 degree above normal

Mean Air Temperature

22.9 degrees C

1.1 degrees above normal

Mean Daily Minimum Air Temperature

21.4 degrees C

1.6 degrees above normal

Mean Dew Point Temperature

18.6 degrees C

2.6 degrees above normal

Mean Relative Humidity

78 %

7 % above normal

Mean Cloud Amount

79 %

25 % above normal

Total Rainfall

73.4 mm

35.8 mm above normal

Number of hours of Reduced VisibilityΔ

40 hours

85.6 hours below normal§

Total Bright Sunshine Duration

123.9 hours

56.2 hours below normal

Mean Daily Global Solar Radiation

10.82 Megajoule / square metre

1.46 Megajoule below normal

Total Evaporation

80.4 mm

19.1 mm below normal

Remarks :

All measurements were made at the Hong Kong Observatory except sunshine,
solar radiation and evaporation which were recorded at King's Park
Meteorological Station and visibility which was observed at the Hong
Kong International Airport.

Δ

The visibility readings at the Hong Kong International Airport are based on hourly observations by professional meteorological observers in 2004 and before, and average readings over the 10-minute period before the clock hour of the visibility meter near the middle of the south runway from 2005 onwards. The change of the data source in 2005 is an improvement of the visibility assessment using instrumented observations following the international trend.
Before 10 October 2007, the number of hours of reduced visibility at the Hong Kong International Airport in 2005 and thereafter displayed in this web page was based on hourly visibility observations by professional meteorological observers. Since 10 October 2007, the data have been revised using the average visibility readings over the 10-minute period before the clock hour, as recorded by the visibility meter near the middle of the south runway.

* Departure from 1981 - 2010 climatological normal, except for number of hours of reduced visibility

§ Departure from mean value between 1997 and 2017

Remarks :

Extremely high: above 95th percentile
Above normal: between 75th and 95th percentile
Normal: between 25th and 75th percentile
Below normal: between 5th and 25th percentile
Extremely low: below 5th percentile
Percentile and 5-day running average values are
computed based on the data from 1981 to 2010